The objectives of this research plan are as follows: 1. Evaluate the functional significance of collateral circulation in the rat kidney during renal artery occlusion. 2. Determine tubular permeability to inulin in rats after partial and complete arterial occlusion. 3. Determine the biochemical effects of partial and complete arterial occlusion with emphasis on membrane functions. Correlate biochemical findings with anatomical observations. 4. Determine the effects of proximal tubular brush border of renal ischemia of varying durations. Study the function of proximal tubules without normal brush borders. 5. Study the mechanism of action in the renal microcirculation by which mannitol alters renal hemodynamics.